In general, kerogen contained in oil shale rocks are pyrolized and recovered in the shape of shale oil by a pyrolysis (retorting) method, wherein such a pyrolysis technique has been applied in common to all the retorting method by mining or the recovering method in a buried state in the field. However, according to such a pyrolysis method, kerogen existing in the shape of hydrocarbon polymer is pyrolized so as to be recovered, wherein the step of heating the oil shale is essentially included. Therefore, there is a disadvantage that 50% or more of kerogen is converted into gas in the heating step or remains as an organic matter having a high boiling point in the oil shale, decreasing the amount of the oil component.
Further, after the shale oil is recovered through the pyrolysis, it is possible to consider the recycling feasibility of the remaining oil shale residue as a soil remediation or construction material. However, there is a problem that, if the amount of the carbon or the organic matters remaining in the remaining oil shale is high, such recycling is impossible. Therefore, the oil shale residue obtained after the shale oil is recovered through such a normal pyrolysis method has been treated to be burned again such that energy is recovered and simultaneously the applicability thereof as a secondary by-product is increased.
However, when applying the additional combustion process to the oil shale residue as above, the possibility of noxious gas emission such as dioxin is increased due to the carbon or the organic matters and the like, which remain in the oil shale residue. In addition, when the oil shale residue is burned at a high temperature, calcium carbonate or magnesium carbonate and the like, which are the main components of the rocks, are thermally decomposed, emitting carbon dioxide that is the greenhouse gas. Therefore, improvement of the existing pyrolysis process is essentially demanded.
In order to solve these problems, the present applicant has been suggested a method for extracting kerogen pyrolysis heavy oil from oil shale by using an extractant or light oil in his prior application (Korean Patent Application No. 2013-0025437). If the oil shale is treated by this method, it is possible to maintain a remarkably higher recovering rate rather than the shale oil recovering rate of the existing pyrolysis process. In addition, it has been recognized that the energy consumption per unit kerogen extraction amount to be recovered and the emission amount of carbon dioxide could be innovatively reduced.
However, it is still technically difficult to completely extract kerogen in the oil shale by this method, which uses an extractant or light oil, and thus part of remaining kerogen pyrolysis heavy oil or a small amount of the extractant/light oil exists in the oil shale residue. Therefore, it has been demanded to provide an economical and effective elimination method for additionally recovering the remaining volatile material such as the remaining kerogen pyrolysis heavy oil or a small amount of the extractant/light oil, existing in the oil shale extraction residue discharged through the extraction method.
Therefore, the present invention is derived to solve the above problems and disadvantages and provides a recovering method for economically treating and recycling the oil shale extraction residue with high efficiency.